Swiss-type or turn-mill: which machine should make your part?
Both machines turn metal round. They are not interchangeable, and putting a part on the wrong one is the most common reason a quote comes back high.
How a Swiss-type actually differs
On a conventional lathe the bar is fed through the spindle and the tool moves along it. On a Swiss-type the bar is held by a guide bushing a few millimetres from the cutting tool, and the bar slides through that bushing as the part is cut. The tool never gets far from the support, so a long thin part does not deflect.
That is the whole point. A 3 mm diameter pin 40 mm long is unremarkable on a Swiss machine and a problem on a conventional lathe, because the guide bushing is doing the work a steady rest would do — but without the setup.
The practical limits
- Bar diameter. Our Swiss line runs φ1 to φ38 mm. Above that the part moves to a turn-mill centre, which covers φ5 to φ200 mm.
- Length-to-diameter. Swiss machines handle long, slender parts well. Turn-mill centres do not, without a tailstock or a steady.
- Feature count on the end face. Swiss machines with a sub-spindle machine both ends in one cycle, which is where the cost advantage comes from on small parts.
- Cross features. A cross hole or a milled flat needs driven tools. Most modern Swiss machines have them; older ones do not.
When the turn-mill wins
Above about φ38 mm, or when the part is short and fat with a lot of milling on it, the turn-mill is the right machine. A manifold body with a turned bore, four cross ports and a milled mounting face is one setup on a five-axis turn-mill and three or four on a lathe plus a mill. Each setup is a datum transfer and a queue.
The other case where turn-mill wins is concentricity between a turned bore and milled features. If they are cut in one setup, concentricity comes from the machine. If not, it comes from your fixture, and fixtures drift.
What this means for your drawing
You do not need to specify the machine. You do need to give the inputs that choose it: bar diameter, overall length, the number of features on each face, and which of those features are critical. With those four we pick the process and quote one number.
What we will not do is quote a part for a Swiss machine because the last part looked similar. The bar diameter alone rules it in or out.